ضمانت نامه و تعمیر و نگهداری پیشگیرانه گسسته

Preventive maintenance actions over the warranty period have an impact on the warranty servicing cost to the manufacturer and the cost to the buyer of fixing failures over the life of the product after the warranty expires. However, preventive maintenance costs money and is worthwhile only when these costs exceed the reduction in other costs. The paper deals with a model to determine when preventive maintenance actions (which rejuvenate the unit) carried out at discrete time instants over the warranty period are worthwhile. The cost of preventive maintenance is borne by the buyer.

All products are unreliable in the sense that they eventually fail. An item failure can occur early in its life due to manufacturing defects or late in its life due to degradation of the item. The degradation is dependent on age and usage. Most products are sold with a warranty that offers protection to buyers against early failures over the warranty period. The warranty period offered has been progressively getting longer. For example, the warranty period for cars was 3 months in the early thirties and this changed to one year in the sixties and currently it varies from three to five years. With extended warranties, an item is covered for a significant part of its useful life. This implies that failures due to degradation can occur within the warranty period. The degradation of item can be controlled by preventive maintenance and this reduces the likelihood of failures. This implies that preventive maintenance becomes important when warranty periods are long. Offering warranty implies additional costs to the manufacturer. This is the cost of repairing item failures (through corrective maintenance) over the warranty period. Preventive maintenance during the warranty period can reduce this cost. Since the buyer pays nothing for repairs during the warranty period, there is no incentive for him/her to invest any effort into preventive maintenance. It is worthwhile for the manufacturer to carry out preventive maintenance only if the reduction in the warranty servicing cost is greater than the extra cost incurred with preventive maintenance. However, from the buyer's perspective, investment in preventive maintenance during the warranty period and after the warranty has expired can have a significant impact on the maintenance cost after the warranty has expired which is borne by the buyer. As a result, buyer's preventive maintenance actions (during the warranty period and afterwards) need to be determined in the lifecycle context. In this paper we develop a framework to study preventive maintenance for items sold with warranty from both buyer and manufacturer perspectives. Such a framework allows one to build alternate models to determine optimal preventive maintenance strategies. The outline of the paper is as follows. In Section 2, we give a brief overview of product warranty and maintenance so as to set the background for the main contribution of the paper. Following this, we develop a framework to study preventive maintenance for items sold with warranty in Section 3. In Section 4, we carry out a review of the literature dealing with warranty and maintenance against this framework. Section 5 deals with the new model formulation and its analysis. Finally, we conclude with some discussions of topics for future research.

In this paper we discussed preventive maintenance which is carried out by the buyer for item sold under warranty and formulated a simple model involving discrete preventive maintenance. We have also discussed for different maintenance level that is carried out during warranty period and after warranty expired as often is the case in real life. The result shows that for large failure costs the optimal result is to carry out different maintenance levels during warranty and after warranty expired. The model can be extended in several ways and we indicate a few 1. The effect of maintenance often leads to the life of the item being extended. This implies that L increases with m. 2. We have confined our analysis to the free replacement policy and failed item being always repaired minimally. The analysis of other types of warranty policies for example, pro-rata, combination is yet to be carried out. 3. We have not studied the different incentive schemes and the related moral hazard issues. This is a topic for considerable new research. 4. We have assumed that the maintenance level is constant. Often, this is not realistic and the maintenance effort changes with the age of the item—less when it is new and more as it ages. 5. We have confined our attention to discrete preventive maintenance effort. Often, one employs both continuous (see Refs. [33] and [34]) and discrete (overhaul) preventive maintenance actions. This makes the problem more difficult and also interesting. Some of these problems are currently under investigation by the authors.